In a crusher of the type to which this invention relates, a generally conical crushing head is mounted on an upright eccentric shaft to be gyrated by rotation of the shaft. On the relatively stationary frame of the crusher there is an annular crushing bowl or concave which more or less overlies and surrounds the crushing head and cooperates with it to define a gap that comprises an annular crushing chamber. Material to be crushed is fed downward through the crushing chamber to be crushed between the bowl and the head as the head gyrates.
One of the problems that has received much attention in the gyratory crusher art is that which arises upon the entry of so-called tramp iron--substantially uncrushable material--into the annular crushing chamber. If the bowl is confined against rising in relation to the head when tramp iron is caught in the crushing gap, there is a high probability of damage to the crushing surface of the bowl or the head, or both, that will put the crusher out of service for a substantial time while the damaged surface is replaced. To prevent such damage, it has been usual to arrange the bowl of a gyratory crusher on an upper frame member that normally rests concentrically upon a fixed lower frame member but can be forced up off of the lower frame member by tramp iron in the crushing chamber. Since the weight of the upper frame member is not great enough to hold it down against the upward forces exerted upon the bowl during normal crushing, it has been more or less conventional to bias the upper frame member downwardly by means of heavy springs whereby the upper frame member was maintained firmly seated on the lower one during normal crushing but was permitted to rise under the greater force developed when tramp iron was present. The springs had to be under a substantial preload by which the bowl was held down, and when the bowl was lifted by tramp iron, this already-high force on the springs was further substantially increased. Usually such a spring arrangement prevented serious damage to the crushing surfaces, but it nevertheless required a fairly prolonged shut-down of the crusher for removal of tramp iron because the spring force had to be relieved and the upper frame member had to be lifted enough to permit the tramp iron to fall through the crushing gap. Relief of spring tension usually entailed the removal of nuts on numerous tie rods that extended through the springs and transmitted spring forces to the upper frame member; and during such disassembly the high energy stored in the springs endangered those doing the work.
The serious and troublesome nature of the tramp iron problem is attested by the relatively large number of patents that have issued on expedients intended to solve it.
One of the earliest of these was U.S. Pat. No. 2,679,984 to Gruender, issued in 1954, wherein the generally conventional springs were replaced by pneumatic pressure cylinder jacks that normally maintained a yielding predetermined downward biasing force upon the upper frame member. The upper frame member could rise under the force exerted by tramp iron in the crushing chamber, increasing the pressure in the pneumatic system, which thus functioned analogously to springs except that pneumatic pressure was not allowed to exceed a predetermined maximum value that was established by a relief valve. For freeing the tramp iron, pressure in the cylinders could be relieved by opening a manually operable valve, and the upper frame member then had to be lifted. Although offering advantages over a spring biased upper frame member, the arrangement could not provide for powered lifting of the bowl when elevation of the bowl became necessary, and it had the further important disadvantage that it needed a large supply of air at high pressure and therefore was not energy efficient.
The employment of single-acting fluid pressure jacks to exert normal downward bias upon an upper frame member was also disclosed in two U.S. patents to Johnson, U.S. Pat. No. 3,118,623 (reissued as U.S. Pat. No. Re. 29,970) and U.S. Pat. No. 3,281,083, and in U.S. Pat. No. 3,038,670 to Becker. In the apparatus of these patents the cylinder jacks functioned in substantially the same manner as the springs that they replaced, except that there was provision for manual relief of the biasing force that the jacks exerted.
In another approach to the problem, disclosed in U.S. Pat. No. 3,140,635 to Balmer et al, springs were employed to bias the upper frame member downwardly in a more or less conventional manner, and manually controlled single-acting fluid pressure jacks were arranged to lift the upper frame member against the biasing force of the springs when tramp iron was caught in the crushing gap. U.S. Pat. Nos. 3,009,660 to Symons et al and 3,162,387 to Symons disclose other arrangements employing the same general principles.
U.S. Pat. No. 2,597,548 to Traylor, Jr., disclosed an arrangement wherein fluid piston devices equipped with one-way bleed valves permitted tramp iron in the crushing gap to lift the bowl against spring bias but whereby downward spring biased return motion of the bowl was retarded to allow time for the tramp iron to pass out of the crushing chamber. In practice this arrangement was not likely to be consistently operative, because the biasing force of the springs increased as the bowl rose, and the tramp iron could not lift the bowl above a level at which it was clear of the tramp iron; hence spring force on the bowl could continue to hold the tramp iron captive in the crushing chamber.
In the crusher of U.S. Pat. No. 3,396,916 to Kemnitz et al, the bowl or concave was surrounded by a cylindrical wall on the fixed lower frame member that cooperated with a cylindrical outer surface on the bowl to define an annular hydraulic cylinder, and the bowl had a circumferential flange which was received in that cylinder to serve as its piston. Pressure fluid in the annular cylinder, above and below the circumferential flange, controlled the heightwise position of the bowl and could be used to raise the bowl for release of tramp iron. The bowl was hydraulically locked at the selected height and therefore could not yield upwardly to any significant extent until a valve in the hydraulic system was manually shifted for raising it.
In the crusher of U.S. Pat. No. 2,791,383 to Kjelgaard, a number of double-acting hydraulic jacks were connected between the lower frame and an upper frame member that comprised the bowl. Fluid under a predetermined pressure was maintained in the lower chambers of the jacks, and fluid that was in effect trapped in their upper chambers held the bowl at a desired height. For adjusting the bowl downward there was a hand pump by which fluid could be forced into the upper chambers of the jacks, and for adjustingly raising the bowl there was a manually operable valve through which the upper chambers could be controlledly drained. Also connected with the upper jack chambers was a pressure relief valve which opened for quickly draining those chambers if pressure in them exceeded a predetermined value--as when tramp iron in the crushing gap exerted an upward force on the bowl--thus automatically raising the bowl for tramp iron release. After each such tramp iron release the bowl had to be brought back down to its operative position by operation of the hand pump. The apparatus had the further disadvantage that any leakage of fluid out of the upper jack chambers allowed the bowl to rise, increasing the width of the crushing gap; and the bowl then had to be readjusted back to a position that was indeterminate in the first place.
U.S. Pat. No. 3,754,716 to Webster disclosed a generally similar arrangement wherein the hand pump of Kjelgaard was replaced by an electrically driven pump and wherein the adjusted position of the bowl was sensed electrically. When the bowl was raised for release of tramp iron, it was maintained in its lifted position for a predetermined period of time and thereafter was brought back down automatically to the electrically sensed position that it had occupied just before being raised. The electrical and hydraulic control system had to be rather complicated because the bowl had no mechanically defined position, and every jack had to be individually controlled in order to prevent the bowl from being established in a tipped position.
U.S. Pat. No. 2,680,571 to Bjarme disclosed a structure wherein double-acting pneumatic jacks were arranged to maintain a normal downward biasing force upon an upper frame member that comprised a concave. There was no provision for automatic relief of the downward bias when tramp iron was present in the crushing gap, but a manually operable valve could be repositioned to so reconnect the jacks that they lifted the upper frame member for release of tramp iron. In common with the arrangements disclosed in certain of the other patents discussed above, the pneumatic jacks in the crusher of the Bjarme patent were located at the top of the crusher, and in fact they projected a substantial distance above the top of the upper frame member. Such an arrangement is undesirable because it adds to the height of the crusher so that the machine is not adaptable to all installations. Furthermore, material to be crushed is fed into a gyratory crusher from above and it must therefore be lifted to a level from which it can fall into the crusher; hence, energy required for feeding material into a crusher is directly related to the height of the crusher. Over the long life of a crusher, and considering that the feed material is usually heavy, every additional inch of crusher height can entail a very significant cumulative energy expenditure.
The above discussed prior patents, and others like them, disclose that there has been a long standing need and desire to provide gyratory crushers with effective means for sensing the presence of tramp iron or other uncrushable material in the crushing gap and for promptly and automatically relieving downward force on the bowl in response to sensing of such material. A basic problem with respect to the provision of such automatically responsive apparatus is that of detecting the presence of tramp iron in the first place. Heretofore, in non-automatic systems, deceleration or stalling of the crusher drive motor has often been relied upon to signal the presence of tramp iron; but by the time rotor deceleration becomes perceptible, a substantial amount of damage can already have occurred. When the upper frame member that carries the bowl is not hydraulically locked against rising, as it was in the above-discussed Kjelgaard patent, an early and significant manifestation of the presence of tramp iron is a tilting rise of the upper frame member. Since such lifting can occur anywhere around the periphery of the crusher, an operator at a fixed control station is not in a good position to observe it immediately and react promptly to it. Any automatic device that provides for a yielding downward force upon the bowl, so that it can be lifted in response to the presence of tramp iron, must likewise take account of the tilting that the bowl tends to undergo when tramp iron is caught in the crushing gap.
It is not imperative that the bowl be positively lifted upon the detection of tramp iron in the crushing gap, to be held high enough for the tramp iron to fall freely through the gap, but an automatic tramp iron release should at least be so arranged that there is no substantial increase in the downward force upon the bowl as it rises, so that the bowl can be lifted by the upward force that tramp iron exerts upon it. On the other hand, during normal operation the bowl should be confined in a defined operative position by a downward force upon it that yields to the lifting action of tramp iron. The normal position of the bowl should be defined in such a manner--preferably by solid abutment means--that the bowl can be brought directly back to it after being so lifted.
It will be apparent at this point that providing for the presence of tramp iron in a gyratory crusher is not a simple problem but instead presents numerous requirements, some of which are in apparent conflict with others. Heretofore no arrangement has been proposed that solves the basic problem and satisfies or resolves all of the requirements and desiderata.